Global positioning systems (GPS) are widely used for navigating ships and aircraft. However, these systems are vulnerable and have other shortcomings. Their space components are subject to hostile attack and the systems may be jammed. The systems also suffer from reliability failures and these GPS systems do not provide absolute azimuth positioning needed for attitude determination. Inertial navigation systems (INS) mitigate GPS deficiencies; however, these inertial navigation systems are not accurate over long time periods. Errors may accumulate at rates of about an arc-sec per hour to an arc-min per hour. Periodic alignment of the inertial navigation systems is required using an external reference system such as a GPS system.
For centuries navigators have used the sky for the most fundamental and accurate inertial system available, in which each star is a benchmark. Cataloged positions and motions of the stars define the celestial reference frame. The problem is stars are hard to see during the daytime. Efforts have been made to navigate by stars during daytime using very sensitive visible light charge couple device (CCD) cameras, but these efforts as far as we know, have been unsuccessful due to the very limited number of stars that can be seen with this sensor.
A need exists for a backup to GPS systems and an absolute azimuth reference for fast alignment of INS systems.